Often, consumer products are packaged in accordance with the following procedure. First, a folded tubular carton precursor is formed from a carton blank by adhering a thin panel called a glue flap, which is appended to a side panel of the carton, to a side panel of the carton. The tubular blank is usually presented in a flattened form to a machine which begins erection of the carton by opening the tube and squaring the carton.
Subsequent to squaring the tubular carton, a first end of the carton is closed by folding the bottom minor flaps inwardly so that they are perpendicular to the side panels. The inner major flap is then provided with a hot melt or other adhesive and folded over the minor flaps. Hot melt or other adhesive is applied to the outer major flap, which is then folded over the inner major flap. Pressure is applied to the outer major flap to effect fully the sealing of the carton. The other end of the carton is then likewise closed by folding the minor flaps so that they are disposed perpendicularly to the side panels, applying hot melt or other adhesive to the inner major flaps, folding the inner major flap over the minor flaps, applying hot melt or other adhesive to the outer major flap, folding the outer major flap on top of the inner major flap, and applying pressure to the outer major flap.
Pressure is generally applied to the outer major flaps during closing thereof by means of a bar or series of bars which contact the surface of the outer major flaps. Unfortunately, application of pressure from a single bar may be uneven. Moreover, even where multiple bars are used, it may not be possible to apply sufficient pressure to all portions of the outer major flap to effect a seal having the necessary integrity for the product contained within the package. Seal integrity can be particularly important for certain types of products such as certain powdered laundry and other detergents.
Application of pressure evenly across the top of the outer major flap is of particular importance in cartons having so called "shied" flaps. In shied flap cartons one or more of the outside and inside major flaps do not extend across the entire width of the carton. This is advantageous in that it conserves paperboard and lowers the cost of the product. However, it will be appreciated that shied flaps will be uneven and that this increases the difficulty in effecting a complete, continuous seal. The problems in effecting a complete seal are particularly acute in the case of the first end to be sealed because the pressure which can be applied is particularly limited since the flaps of the opposite end are still open and cannot bear much weight.
Apart from "shied flap" cartons, producing an effective seal is also particularly difficult for cartons which for any reason have a top or bottom surface which is not flat.
Equipment utilizing stationary, individually adjustable bars for sealing cartons is known.